Cell injury or death may occur by a variety of potential mechanisms including damage to macromolecules like DNA or proteins, and derangement of organelles like ribosomes, mitochondria, r membranes. This proposal is concerned with the role of one of these targets, the cell surface membrane, in mediating cytotoxicity. The cytotoxic agents chosen for intensive study are anthracyclines. These compounds represent a good model system because: (a) extensive evidence exists showing that the anthracyclines are extraordinarily active at modulating membrane functions, and (b) these compounds can, under certain conditions, be actively cytotoxic without entering cells. This application describes experiments intended both to further certify the hypothesis that the cell surface us a sensitive target for cytotoxic action and to yield insight into the fundamental mechanisms involved in plasma membrane- mediated cell kill. Three aims are proposed. First, the temperature dependence of adriamycin action will be studied. We have found that adriamycin loses its activity below 20 degrees celsius. This loss of cytotoxicity appears to be linked to the ability of drug to damage DNA, but the response is initiated by a plasma membrane interaction. Further studies will define the role of protein kinase C, DNA repair, and membrane physical structure in this pathway. The second aim is intended to address the hypothesis that the mechanism of adriamycin cytotoxicity involves the modulation of normal growth regulatory and signal transduction processes occurring on the cell surface. We have shown that the drug causes an up regulation of the receptors for epidermal growth factor, and we plan to study the linkage of this event with drug action by examining alterations in receptor phosphorylation and dimerization. The third aim is to provide further insight into the unexpected ability of anthracyclines to stimulate DNA synthesis and proliferation at low, subtoxic concentrations. This finding has led us to hypothesize that cytotoxicity and stimulation of growth may occur by similar initiating mechanisms. We plan to test this idea by studying the ability of adriamycin to modulate c-fos expression in quiescent cells, looking at both induction of message levels and the response of cells transfected with an antisense fos gene.